Just 10 years ago (but we could also say just a little over 5 years ago), the different tiers described previously were usually filled with the following types of storage:

• Tier 0: 15K RPM Serial-Attached SCSI (SAS) disks
• Tier 1: 10K RPM SAS disks
• Tier 2: 7K RPM SATA or nearline disks
• Tier 3: Usually tapes

Traditional Hard Disk Drives (HDD) were the standard components for storage arrays, and more were used both for redundancy and for increasing performance. RAID hardware was the standard at the beginning, surpassed by a more software controlled style of data management.

The typical interface and bus for those hard disks is SAS, working at 6 or 12 Gbps. SATA disks use the Serial ATA (3.0 revision works at 6 Gbps).

Anyway, spinning disks are still relevant and used, and new improvement has been achieved to increase density, performance, and reliability; for example, the perpendicular recording (2006) and the Advanced Format (2011) technologies. The second one is quite important because it can work in two different modes—legacy 512e or native 4K. Windows has supported 4K mode since Windows 8 and Windows Server 2012, and Linux since kernel version 2.6.31. ESXi 6.5 is now supporting this new technology, but only in 512e mode.

See also KB 2091600—Support statement for 512e and 4K Native drives for VMware vSphere and vSAN (https://kb.vmware.com/kb/2091600).